Many compounds that have low solubility in water (e.g., compounds that have a solubility of less than 1%) have other properties that make them particularly appropriate for use in aqueous systems. For example, many solid halogen donor materials such as halogenated hydantoins have low solubility, but are effective and economical biocides for recreational and industrial water systems. Similarly, non-biocides such as cyanuric acid have low solubility but are effective UV stabilizers for halogen source materials.
More particularly describing the halohydantoins, solid halohydantoins such as bromochlorodimethylhydantoin (BCDMH) have been used to sanitize waters for many years. Unfortunately though, many solid halogen donors and all of the halohydantoins have low water solubility, slow dissolving kinetics and are hydrolytically unstable. The water solubility for BCDMH, for example, is low, approximately 1,500 mg/liter at 20.degree. C., and it dissolves slowly, depending on surface area, contact time and water temperature.
Moreover, dissolved BCDMH is not hydrolytically stable because it hydrolyses to yield dimethylhydantoin and the biocidal hypohalous acids, hypochlorous acid and hypobromous acid, which in turn degrade to the respective halides, chloride and bromide, within hours.
Solid halogen donors are available as solids in powdered form and also in various compressed forms such as granules, tablets or briquettes. These are dosed to treated water systems by several means, each of which is labor intensive and exposes workers to the solid product. Among the dosing methods are:
1. Manual broadcasting of product onto the water surface with product dissolving directly in the system. The amount of product used in the broadcasting system can be accurately measured. However, the rate at which the product dissolves will vary with water temperature, mixing and product form. If the product dissolves too slowly, the concentration in the system water may not reach a high enough level to be effective. Locally high concentrations and undissolved product in contact with system parts can cause compatibility problems in some systems.
2. Submerged porous containers or product in the water with product dissolving directly in the system. This approach eliminates direct contact of the product with system parts but there may still be problems associated with locally high concentrations. It is more difficult to control how much product dissolves in the system with this method because the concentration will be dependent on water temperature, mixing and product form so the product may be overdosed or underdosed.
3. Bypass feeders use a fresh, or system, water stream to dissolve product by passing through a product bed in the feeder. This concentrated solid halogen solution is subsequently diluted into the system being treated. This method typically eliminates system material compatibility problems. However, feed consistency does vary with bypass water temperature, contact time (feeder volume, water flow and quantity of product in the bed) and product form. The level of product in the bypass feeder must be maintained for consistent feed and the water flow rates need to be adjusted to compensate for any temperature variations. There may be problems associated with extra water being added to some systems if system water is inappropriate for use in the bypass feeder.
4. Slurry feed is a method where product is mixed with a fresh, or system, water stream to create a slurry (typically less than 3% of the solid halogen donor) which is subsequently diluted into the system. This method can very accurately meter the required quantity of product and eliminates dependence on water temperatures or very accurate control of water flow rate. This equipment can be expensive and there may be problems associated with extra water being added to some systems if system water is inappropriate for the bypass stream.
As to some other low solubility water additives that are appropriate for use in the present invention, terbuthylazine, [2-(tert-butylamino)-4-chloro-6-(ethylamino)-s-triazine], is used as an algae control agent in water either alone or, synergistically, with oxidizing halogen. More detail regarding this type of application may be found, for instance, in Impact of Cooling Water Treatment Trends on Algae Control by J. F. Kramer Off Proc.--Int. Water Conf. (1995),56.sup.th, 449-456. It is also useful for stabilizing halogen in water systems as described in EP 857694 Method for Stabilizing Disinfectant in Aqueous System, by J. F. Kramer and F. O'Brien (1998).
The US-EPA Registration Eligibility Decision (RED) document published in December 1997 (available electronically at www.EPA.gov) indicated that the solubility for terbuthylazine is 11.5 ppm at 25.degree. C. with use levels between 1 and 9 ppm. Terbuthylazine has good hydrolytic stability with degradation half lives of 73 days at pH 5,205 days at pH 7 and 194 days at pH 9.
The product is available as a 96% wettable powder (Bellacide.RTM. 320), as well as a 44.7% aqueous dispersion (Belclene.RTM. 329) and a 4% aqueous dispersion (Bellacide.RTM. 325). The product brochure from FMC entitled Bellacide.RTM. 325 An Effective Algal control Agent Recommended for Recirculating Cooling Water Systems and Decorative Fountains recommends product addition at a point in the system where there is good mixing such as in the cooling tower sump near the recirculating pump.
It would be advantageous if an easily pumped concentrated aqueous formulation of terbuthylazine were available with an improved rate of dissolution, because the solubility limit for terbuthylazine (11.5 ppm) is so close to the required treatment range (1 ppm to 9 ppm).
As to other low solubility biocides, 2-(2-bromo-2-nitro)-ethenyl furan (hereinafter BNEF) is useful for controlling algal, fungal and bacterial growth in water systems. Its manufacture and use have been described in several U.S. Pat. Nos. such as 4,965,377; 5,138,078; 5,090,990; 5,045,104; 5,246,943; 5,358,963; 5,416,107 and 5,416,108. BNEF decomposes rapidly in water; at 25.degree. C. the decomposition half-life is 71 hours at pH5, 37 hours at pH 6 and 6 hours at pH 9. Decomposition occurs even faster at higher temperatures; at pH 4 the decomposition half-life is 140 minutes at 50.degree. C., 106 minutes at 60.degree. C. and 49 minutes at 70.degree. C. Even though BNEF is not very hydrolytically stable, this non-oxidizing biocide kills rapidly so that it is effective if the proper amount can be dissolved in water. However, this material is only marginally soluble in water, 300 ppm at 25.degree. C. This low water solubility, along with rapid decomposition can make it difficult dissolve the desired level of active ingredient. U.S. Pat. No. 5,122,301 by McCoy et. al. describes the preparation of a soluble formulation containing 10% BNEF in an organic solvent, propylene carbonate. Dosing systems with BNEF with this formulation will result in organic contamination.
It would be advantageous if an easily pumpable concentrated aqueous formulation of BNEF were available with a rapid dissolved rate.
As to non-biocidal water additives with low solubility, Isocyanuric Acid (hereinafter "CYA," and also referred to as S-triazine-2,4,6-trione), is used in water treatment to stabilize oxidizing halogen against decomposition. This is described in the Professional Pool an Spa Technicians' Guide to Chlorine by R. W. Lowry and D. Dickman (1989), Service Industry Publications, Inc. This publication suggests adding CYA granules by sifting or broadcasting them over the surface of the deep end of the pool. It states that the granules are fairly tough to dissolve and often sit on the bottom of the pool for as long as a week. Alternatively, the granules can be "dissolved" in warm water with soda ash and added to the pool by "walking" the solution around the pool.
The solubility of CYA in water is approximately 2700 ppm at 20.degree. C. CYA is typically supplied as a 99% to 100% pure granular material. In addition to water treatment, CYA has uses as a chemical intermediate in the manufacture of resins, plastics additives and coatings. For the reasons noted above, it would be advantageous if easily pumped, rapidly dissolving concentrated aqueous formulations of CYA were available.
As indicated above however, it is impractical to prepare aqueous solutions of the above-mentioned water additives (and others with similar characteristics) because these products exhibit low water solubility, slow dissolving kinetics and are hydrolytic unstable. Moreover, many organic solvents are not compatible with solid halogen donors, and even if they were, it is undesirable to add organic solvents to water systems because they contaminate the water, contribute to undesirable biological activity, and require additional waste water treatment prior to discharge.
In view of the above a need continues to exist for concentrated aqueous dispersions of low solubility and/or low stability water additives. The present invention addresses that need.